The goal of the symposium and associated workshop is to catalyze new interdisciplinary research directions on biotic exchanges between saline and fresh habitats and how they profoundly shaped life. Specific objectives include:

1. Reveal halohabitat transitions. We will chronicle episodes of biotic exchange between marine and freshwater that are shared by multiple major taxa, and those that are unique to a taxon. Questions include:
   1. When did major colonizations of fresh waters happen?
   2. What physiographic changes facilitated transitions?
   3. How frequently have freshwater taxa returned to marine habitats?
   4. How porous is the boundary?
2. Document biotic transformations. We will identify common processes underlying diversification and adaptation in multiple taxa arising from changes in halohabitat. Questions include:
   1. Have transitions impelled diversification?
   2. How do organisms adapt physiologically to change in halohabitat?
   3. How do marine and freshwater lineages differ in morphology, life history?
   4. What differences in community-level processes and ecosystem services arise from these transformations?
3. Contrast current threats. We will utilize these interactions and transitions to better understand responses to global change in each realm. Questions include:
   1. In what ways are the freshwater and marine forms subject to different anthropogenic stressors?
   2. How are present-day global changes in the environment influencing halohabitat and how are organisms contending with them?